Synthetic resin enamel stripping compositions



United States Patent 2,737,465 Y SYNTHETIC RESIN ENAMEL STRIPPINGCOMPOSITIONS Leopold lessel, Philadelphia, 12:1,, assignontoRadiofCorporationofiAinerica, ,a corporationof Delaware:

No Drawing. Application May- 28; 1948, Serial No. 29,93 1

13 Claims. (Cl. 1344-38) This invention relates, generally, tocompositions for: stripping synthetic resin. coatings from varioussurfaces and; more particularly,-relates to improvements in compositions. whichhaveespecial utility-in removing insula,- tionifrorncopper wire, at thezsame time preparing the wire to receive a coat ofsolder.

In the electrical industries, it is frequently necessary-to stripcoatings comprising synthetic resinous.- materials from the ends ofwires preparatory to soldering them to terminals or to other, wires.This necessitates a great deal of hand labor by skilled operators and,in the case ofcertain' insulation materials, such as polyvinyformal,

it is an expensive and'tim'e consuming 'p'rocediir'e'. The. presentinvention relates to improvements a p series"of-composition'swhichmay beusedtos H H the most-resistantsynthetic resin materials in a" matteroffjseconds. These compositions leave the wire base in aclean and brightstate to which a layer of solder may immediately be applied withoutsubjecting the Wire to any further'treatment such as the application ofa flux.

The methodsdescribed. in. the presentapplicationarl closely relatedto.those disclosed. in co:-pendinge-applica'- tion, Serial No. 744,775,filed April 29.,.1.947.,.Patcnt:':No. 2,563,417, Aug..7, 1951, by. thepresent inventorz" ms materials disclosed herein are improvements in thecompositions disclosed in the said application, in that they are stillfaster in action. In the previous application, there were. disclosed:compositions containing pentanedione 2,4, with or without a certainamount ofwatenand preferably. containing a'mutualsolvent forthepentanedione 2,4. and the water. It-hasnow been foundthatif:

formic acid or. certain. formic. acid, derivatives-' be substitiite'dl'for part of the pentanedione 2,4, thesm'pping action of thecomposition is fspeeded. up considerably,--enablingit to be used inconnectionfwith automaticstrip ping machines. derivative found useful'in the present invention, the-fume removal problem is not serious andthe compositions do; not. introduce any objectionable healthhazardatqthe,

workers. 7

One object of the present invention-is to provider'improvementsiincompositions-containing pentanedione 2,4 for stripping anysynthetic resin coating froma base.

Another object of the present invention is to provide improvedcompositions for-facilitating the-stripping of synthetic resin coatingsfrom a wire-base.

Another objectis to provide improved compositions theveryrapidsofteningof synthetic, resinous' materials" comprising oneormore-of the polyvinylacetalseriesr' Another object of thepresentinven'tion is the provision of improved compositions forstripping synthetic, resinous With the percentages ofv formic. acid.

2,737,465 Patented M51216; i956 the present inventioin may be used isillustrated in the following example. The end of a coppermagnet wire; na n a h n ng. of e vinyla s l sy the resin,-isdip ped in av bath ofthestrippjng agent; main; tained at l7 5 F., untilthe coating is,softened, The i e s: mov om the q i en l n essui is 3P: p1ib n S of theum and otefi s i ndhe ns' .-,.n t be t z r t a s n le. motion...Automatic machines may also be used ton ap; plyin g the pressure to thecoating and pullingit from-the; endof the wire. The end of the wire fromwhich the coating hasbeen removed is then dipped immediatel a tinningorsoldering bath of conventional composition, which provides it with aclosely; adherent coating; of,

metal. which. does not deteriorate: on long standing,-

thewire. This tinned or soldered} end mayzthen be: mediately. soldered.to a. terminalfor tofanotl er, wirewithnolfurther treating The solderbath m ay be et) pepper-1t; tin and 40 per centleador 40 percenttintandfifl pe cent lead or. of. any. other conventional soldercompositi 5.

The time of treatment necessary to soften. the :coatip'gi,materialisuificiently to be strippedoif with; a single motionyariestwith the temperatureof the-bath. v g

The preferred compositions, accordingto, the present invention, arethose which contain pentandione 2,4, formic acid and at least'a smallamountofrwater. Use of: a: mutual solvent for the pentanedione 2,4 andthe waterproduces equally good results. The pentaned ione 2,4 shouldv bepresent in the range ofi'about; 30"t6fabout 9,8.v volume per cent.Concentrated formic acid of tor9 O'vpercent strength may be present inthe range of about 2-to about 50-volume per cent. Providednhafat least 2percent of'the composition:is concentrated formic} acid of 85.'to percent strengthandat'least SOQVQlnrnei' per cent of the composition ispentanedione 2,4, the ref mainder'of the'volume may b'eJmadeup byaddingwatei or' mixtures of water with" an organic solvent mutuallycompatible with Water and pentanedione. 2,4. Composi,-; tions withintheabove range are'muchmore rapid irI' their stripping action thaneither thesamesconcentration; of the pentancdione 2,4, by itself,orconcentrated formic acid in the indicated percentage range,dilutedonlywith water, or the water-solvent mixture, by itself.

Since it is desirable to have compositions which will notseparate intotwo phases at room temperaturegcompositions are preferred which have thedesired rapid treatingtirhe at practical elevated temperatures andremain in a single phase even after standing at room tern; peratures of70 R'for long periods of time. It has be n, found that mutual solventsfor pentanedione 2,4 and} watermay be added to the system withoutchanginglthej.

Although. many different types of mutual solvents for pentanedione 2,4and water were tried, none was found which had any adverse efiect, theirinclusion, when used in amounts up to 25 per cent, not slowing down thesoftening effect of the pentanedione 2,4 and water enough to make theiruse impractical. Besides diacetone alcohol, other ketones, such asacetone, acetonyl acetone, etc., are almost equally applicable. Esters,such as methyl lactate, ethylene-glycol-rnonoethyl-ether, ethyl lactate,etc., may be used. Alcohols, such as ethyl alcohol, isopropyl alcohol ortetrahydrofurfuryl alcohol, or others, besides diacetonealcohol, havebeen found almost equally advantageous, while other miscellaneous mutualsolvents for pentanedione 2,4 and water, such as gammavalero lactone,propylene oxide and dioxane have all b'n tried and found operative.Although the invention is perhaps most valuable when used with suchcoatings as the polyvinyl acetal resins or with polymerized oil-resinenamels, since these are extremely diflicult to remove by means formerlyin use, these softening agents exert a dissolving or a softening actionon synthetic resins in general and have useful application in preparingany wire coated with a synthetic resinous material for the applicationof solder. Besides those resins already mentioned, there have been usedresins of the phenolic type, such as phenol formaldehyde, polymerizedallyl esters, copolymers of styrene and allyl esters, furane resins,superpolyamides, alkyds, melamine formaldehyde, etc. Although some ofthese resins may be softened -with other solvents, it is advantageous tobe able to soften them rapidly with a material which leaves no unwantedresidue after the coating is stripped from the wire and, in general, thecompositions of the present invention are considerably faster in action.

The following table shows the effect on a number of different types ofresin coatings of compositions made up according to the presentinvention, the time given being that required to soften the resinsufficiently to be stripped off in a single motion:

2 or c Pentane- Acid10 gg Type of Coating 2 Seconds Boosting FactorPolyvinyl Acetal 180 30 6.0 Phenolic Resin- 50 20 2. 6 do 150 30 5. 0 do180 30 5.0 Silicone Resin 30 10 3. 0 Allyl Ester Resin 240 30 8. 0stiyrene Copolymer Res- 30 6. 0

. Furane Resin 300 60 5.0 Polymerized Oil En- 25 2. 5

ame 30"; Superpolyamide-.-- 4, 000 60 67. 0 Al Sheet; Alkyd TypeEnamel... l0 5 2.0 Glass Rod. Melamine Formalde- 60 10 6.0

hyde Resin.

Wood Pane1 ,do 80 5.3

The above table shows the softening time for various resins with thecomposition maintained at150 F. and shows the' comparison between usingpentanedione 2,4, alone, and compositions in which some of thepentanedione 2,4 has been replaced with formic acid. The boosting factoris obtained by dividing the softening time with pentanedione 2,4, alone,by the softening time required for the corresponding resin compositionwhen using the composition with the formic acid added. This table alsoindicates that the compositions of the present invention are useful notonly in stripping resin coatings from wires but from other surfaces,such as aluminum sheets, glass rods or wood panels. The surfaces listedare merely illustrative and may comprise anything to which syntheticresins are commonly applied as coating materials.

The data given in the above examples were obtained,

using coatings of comparable thickness on commercially available magnetwires. It is quite obvious that the thickness of the coating willinfluence the speed of softening; the thinner the coating, the morerapid the softening action, providing the same diameter of wire is used.For unexplained reasons, in extremely thin wires, an increase insoftening time has been found with decreased wire diameter.

It has been noted that the boosting effect of the water on the softeningaction of the pentanedione 2,4 increases practically in directproportion to its content in the compositions up to 50 per cent water orhigher but, when using the higher percentages of water, it is necessaryto raise the temperature of the compositions to inconvenient points inorder to prevent the separation of the mixture into two phases. None ofthe mutual solvents for water and pentanedione 2,4 which have been usedin the compositions, when used alone, has been foundto have anysignificant softening effect on the resistant types of resinousmaterials.

In general, the optimum amount of mutual solvent to be added to thecompositions varies with the mutual solvent selected. In a compositioncomprising pentanedione 2,4 and water in a 2:1 ratio, for every 1 partsof diacetone alcohol, for example, there would be needed only 0.8 partof isopropyl alcohol, 0.7 part of tetrahydrofurfuryl alcohol but 1.4parts of gamma-valero lactone. The addition of more than the optimumamounts of the various mutual solvents exerts a diluting effect and suchproportions may be used to lower the cost of the resulting compositions.

Examples of preferred compositions made up according to the presentinvention will now be given:

' The composition of Example II is somewhat more rapid in its actionthan that of Example 1.

Although formic acid, itself, has been used as a stripping agent forsome time, if formic acid, by itself, is to be used for this purpose,percentages considerably above 50 per cent formic acid must be used toobtain stripping efficiency. When such higher concentrations are used,however, a number of undesirable features are introduced,

such as danger and annoyance due to fumes and contact of'the liquid withthe human skin, absorption of the formic acid in'the unstripped portionof the coils with resultant corrosion. Compositions of the presentinvention, since they enable such low percentages of formic acid toberused, avoid these shortcomings.

It is to be emphasized that the percentage of formic acid used inaccordance with the present invention is always less than .50 volume percent. Percentages of formic acidused in this invention may be so lowthat an equivalent percentage in an aqueous solution, Without the use ofpentanedione 2,4, would be utterly ineifective for the purposesintended. This may be demonstrated by the figures given below whichindicate immersion periods in seconds required to render a certain typeof Seconds required to soften A stripping agent containing:

Pentaned1one2,4 volume percent 50 Water a (10..-. 25 Diacetone-alcohol..do 25 27 100 Pentanedionezn do 40 Water 7 do.- 20 Diacetonealcohol....do 20 15 85%formicacid .do 20 100 Pentanedionetpi do 20 1 Water I v-do- 20 Diace'tonealochol; do'. 20 n 85% formic acid do 40 100 85%formic acid do. 40 Water .do.. 60 30 100 85% formic acid do.... 210Water do. 80 (1) 100 I Inactive after 60.

From the above examples, it may be seen that the addition of formic acidto a system containg pentanedione 2,4 and water unexpectedly increasesthe speed of the stripping action to a point considerably above that ofeither straight pentanedione 2,4 solutions or comparable formic acidsolutions.

There is an indication that the effect of the formic acid on theefficiency of the stripping solutions is linked with the molecularstructure of this compound. It has also been found that formic acidderivatives show a similar boosting effect on the speed of action. Forexample, a composition containing pentanedione 2,4, 98 volume per cent,concentrated formaldehyde solution, 2 volume per cent, has a strippingefiiciency 50 per cent higher than straight pentanedione 2,4, while acomposition containing pentanedione 2,4, 90 volume per cent,concentrated formaldehyde, volume per cent, has an efficiency thricethat of straight pentanedione 2,4. In comparison With the rapid actionof compositions comprising pentanedione 2,4 and formaldehyde,formaldehyde-water compositions containing as much as 20 per centconcentrated formaldehyde are completely inactive in removing mostsynthetic resin insulation materials. The optimum amount of formaldehydefound useful in the compositions containing pentanedione 2,4 is about 5to 10 per cent formaldehyde to 90 to 95 per cent pentanedione 2,4.Useful effects, however, have been found by using as much as 50 per centformaldehyde with 50 per cent pentanedione 2,4. It was found that usingan optimum composition of pentanedione 2,4 and formaldehyde on a givenpolyvinyl acetal coating that the time required for stripping was onlyone-fourth that required by pentanedione, alone.

Formamide has no stripping effect, whatever, by itself, in aqueoussolution, but when combined with pentanedione 2,4-water systems, thereis a definite booster effect found when amounts up to 50 per centformamide are used. The optimum percentage is about 20 to 30 per centformamide to 70 to 80 per cent pentanedione 2,4. The highest boostingfactor obtainable with formamide is about 6 compared with pentanedione2,4, alone. That is,the time required to strip a given polyvinyl acetalenamel from a given diameter wire is about one-sixth that required usingpentanedione 2,4 without the added formamide.

The esters of formic acid also have a boosting effect on the strippingaction of pentanedione 2,4 or pentanedione 2,4 and water, although theeffect is much weaker than that of formic acid or formamide, forexample. Such esters may be methyl, ethyl, n-propyl, or n-butyl formate,etc., or esters such as ethylene diformate or benzyl formate. In fact,any alkyl or aryl group may be present since the action appears to bedue to the formyl group and not to the remainder of the molecule. As anexample, a compositionv containing, pentanedibne 2,4,. volume per cent,and methyl formate, 20 volumeper cent, strips; a given polyvinyl. acetalenamel in, one-half I the time requiredfor pentanedione, alone. p

In general, it has beenfol d. hat: those-formic acid, derivatives.having. the, formula,

X in which X may be H, O-.H, .-NHz i or where Risany alkyl; or. a-rylgroup are. prefer-red. Since;

theimprovement appears t be due to the /H C=O group however, theremainder of the molecule does not appear to make much difference exceptthat some exert more boosting effect than others. In general, also, ithas been found that these boosting agents should be present in amountsranging from 2 to 50 volume per cent for best results although withsome, higher amounts exhibit a somewhat increasing effect in proportionto the amount used.

There have, thus, been described improved liquid compositions forstripping a synthetic resinous composition from any surface to which itnormally adheres. The stripping compositions comprise pentanedione 2,4and either formic acid or a formic acid derivative. The stripping actionis brought about by a rapid softening of the coating being removed. Theuse of the improved compositions introduces no health hazard and theiruse is simply and easily carried out. It will be obvious that thepreferred mode of carrying out the invention as described is susceptibleof various modifications but it is intended that the invention belimited only as defined in the appended claims.

I claim as my invention:

1. A composition for softening synthetic resinous coat ings consistingessentially of about 30 to about 98 volume per cent pentanedione 2,4,about 2 to about 50 volume per cent of a compound selected from thegroup consisting of formic acid, formaldehyde, formamide and esters offormic acid, and which contains up to 68 Volume per cent water.

2. A composition according to claim 1 in which said compound is formicacid.

3. A composition for softening synthetic resinous coatings consistingessentially of about 30 to about 98 volume per cent pentanedione 2,4,about 2 to about 50 volume per cent of a compound from the classconsisting of formic acid, formaldehyde, formamide and esters of formicacid, and up to 68 per cent water and a mutual solvent for pentanedione2,4 and water.

4-. A composition according to claim 3 in which said compound is formicacid.

5. A composition according to claim 4 in which said mutual solvent isdiacetone alcohol.

6. A composition according to claim 5 containing about 2 to about 20volume per cent formic acid, about 30 to about 50 volume per centpentanedione 2,4, and up to about 48 volume per cent of equal parts ofwater and diacetone alcohol.

7. A composition according to claim 6 containing 20 volume per cent ofconcentrated formic acid, 40 volume per cent pentanedione 2,4, 20 volumeper cent water and 20 volume per cent diacetone alcohol.

8. A composition for softening synthetic resinous coatings consistingessentially of 30 volume per cent pentanedione 2,4, 40 volume per centof 85 concentrated formic acid, 15 volume per cent water and 15 volumeper cent diacetone alcohol.

9. A composition for softening synthetic resinous coatings consistingessentially of pentanedione 2,4 and about 2 to about 50 volume per centformaldehyde.

10. A composition according to claim 9 in which said formaldehyde ispresent within the range of to 10 volume per cent.

11. A composition for softening synthetic resinous coatings consistingessentially of pentanedione 2,4 and about 2 to about 50 volume per centformamide.

12. A composition according to claim 11 in which said formarnide ispresent within the range of to volume per cent.

13. A method of softening a synthetic resinous coating comprisingsubjecting said coating to a composition consisting essentially ofpentanedione 2,4 and a compound selected from the group consisting offormic acid, formaldehyde, formamide and esters of formic acid, saidcomposition being maintained at a temperature of to References Cited inthe file of this patent UNITED STATES PATENTS 871,750 Austen ct al. Nov.19, 1907 1,095,270 Ellis May 5, 1914 1,884,765 Lougovoy Oct. 25, 19322,435,239 Schub Feb. 3, 1948 2,507,985 Kuentzel May 15, 1950 2,563,417Pessel Aug. 7, 1951 OTHER REFERENCES Gregory: The Condensed ChemicalDictionary, 3rd edition, Rheinhold Publ. Corp., 1942, page 45, column 1.

1. A COMPOSITION FOR SOFTENING SYNTHETIC RESINOUS COATINGS CONSISTINGESSENTIALLY OF ABOUT 30 TO ABOUT 98 VOLUME PER CENT PENTANEDIONE 2,4,ABOUT 2 TO ABOUT 5 VOLUME PER CENT OF A COMPOUND SELECTED FROM THE GROUPCONSISTING OF FORMIC ACID, FORMALDEHYDE, FORMAMIDE AND ESTERS OF FORMICACID, AND WHICH CONTAINS UP TO 68 VOLUME PER CENT WATER.
 13. A METHOD OFSOFTENING A SYNTHETIC RESINOUS COATING COMPRISING SUBJECTING SAIDCOATING TO A COMPOSITION CONSISTING ESSENTIALLY OF PENTANEDIONE 2,4 ANDA COMPOUND SELECTED FROM THE GROUP CONSISTING OF FORMIC ACID,FORMALDEHYDE, FORMAMIDE AND ESTERS OF FORMIC ACID, SAID COMPOSITIONBEING MAINTAINED AT A TEMPERATURE OF 150* TO 175* F.